13 cities
| City | Rank | 2025 Pop. ↓ | 2020 Pop. | Change | Density | Area (mi²) | Type |
|---|---|---|---|---|---|---|---|
| Lower Brule | 1 | 962 | 971 | 2.56% | 2,650 | 0.36 | CDP |
| West Brule | 2 | 664 | 383 | 7.1% | 562 | 1.18 | CDP |
| Presho | 3 | 460 | 469 | -0.43% | 686 | 0.67 | City |
| Oacoma | 4 | 392 | 386 | 0.26% | 150 | 2.61 | Town |
| Kennebec | 5 | 288 | 278 | 0.7% | 338 | 0.85 | Town |
| Vivian township | 6 | 129 | 123 | 1.57% | 4 | 36.09 | Township |
| Reliance | 7 | 126 | 128 | 0% | 116 | 1.09 | Town |
| Oacoma township | 8 | 80 | 81 | 0% | 1 | 59.86 | Township |
| Iona township | 9 | 64 | 65 | 0% | 1 | 127.89 | Township |
| Vivian | 10 | 33 | 87 | -13.16% | 19 | 1.73 | CDP |
| Rex township | 11 | 23 | 23 | 0% | 1 | 35.83 | Township |
| Pratt township | 12 | 19 | 19 | 0% | 1 | 25.54 | Township |
| Bailey township | 13 | 13 | 13 | 0% | 0.00 | 43.42 | Township |
Lower Brule is the largest city in Lyman County, with a population of 962.
Bailey township is the smallest city in Lyman County.
There are 13 cities in Lyman County, South Dakota.